Liquid crystal display device

ABSTRACT

A liquid crystal display device includes a TFT substrate having a display region with first and second electrodes, TFTs, scanning signal lines connected to the TFTs, a counter substrate, a liquid crystal layer sandwiched between the TFT substrate and counter substrates, and sealed by a sealant, scanning line leads connected to the scanning signal lines and formed outside of the display region, video signal line leads connected to the video signal lines and formed outside of the display region and a shield electrode formed on the TFT substrate covering the scanning line leads but not the video signal line leads. The second electrode is connected to a TFT, and liquid crystal molecules of the liquid crystal layer are driven by an electric field, which is generated between the first and second electrodes. The shield electrode is electrically connected to the first electrode and overlapped with the sealant in plan view.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.14/491,416, filed on Sep. 19, 2014 (now U.S. Pat. No. 9,041,893), whichis a continuation of U.S. application Ser. No. 14/145,321, filed on Dec.31, 2013 (now U.S. Pat. No. 8,867,011), which, in turn, is acontinuation of U.S. application Ser. No. 13/569,484, filed on Aug. 8,2012 (now U.S. Pat. No. 8,634,049), which, in turn, is a continuation ofU.S. application Ser. No. 12/430,973, filed on Apr. 28, 2009 (now U.S.Pat. No. 8,248,568), the entire contents of which are incorporatedherein by reference.

CLAIM OF PRIORITY

The present application claims priority from Japanese Patent ApplicationJP 2008-116981 filed on Apr. 28, 2008, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention concerns a display device and, particularly, itrelates to a liquid crystal display device of an in-plane electric fieldsystem (IPS) excellent in view angle characteristics with no imageunevenness also at the periphery of a display region.

2. Description of Related Art

In a liquid crystal display device, a TFT substrate having pixelelectrodes and thin film transistors (TFT) formed in a matrix and acounter substrate opposed to the TFT substrate and having color filters,etc, formed at portions corresponding to the pixel electrode of the TFTsubstrate are disposed, and liquid crystals are put between the TFTsubstrate and the counter substrate. Then, images are formed bycontrolling the transmittance of a light by liquid crystal molecules onevery pixel.

Since the liquid crystal display device is flat and light in weight,application use thereof has been extended in various fields. Small-sizedliquid crystal display devices are generally used for cellular phones,DSC (Digital Still Cameras), etc. In the cellular phones and DSC, thereexists a demand of enlarging the size of the display screen whilekeeping the outer shape of a liquid crystal display device small. Then,a so-called frame at the periphery of the display region is reduced. Insuch a constitution, the periphery of the display region tends toundergo the effect of potential fluctuation at, etc. at the frameportion.

On the other hand, view angle characteristics become a problem in theliquid crystal display devices. The view angle characteristics concern aphenomenon that the luminance or chromaticity changes between a case ofobserving a screen at the front and a case of observing the screenobliquely. For the view angle characteristics, an IPS (in planeswitching system) of operating liquid crystal molecules by an electricfield in a horizontal direction has excellent characteristics.

Japanese Unexamined Patent Publication No. 2005-275054 describes aliquid crystal display device of the IPS system in which a taperedportion of scanning line leads is covered with a conductive film by wayof an insulative film so that blanking does not occur at the peripheryof a display region by noises from the scanning line leads. That is, apitch in the terminal portion for connecting the scanning lines withexternal circuits is smaller than the pitch of the scanning lines formedin the display region. Then, the scanning line leads that connect theterminal portion with the scanning lines of the display region are inthe form of oblique (tapered) wirings for adjusting the pitch betweenthe display region and the terminal portion. In the oblique wiringportion, since the wiring density is higher than that in the displayregion and noises due to scanning signals tend to be generated, it isintended to cover the portion with the conductive film thereby reducingthe effect of the noises from the tapered portion in JP-A No.2005-275054. For the conductive film, ITO (indium tin oxide) which isidentical with that used for the pixel electrode is used.

In the constitution descried in JP-A No. 2005-275054, the scanning linelead is covered with ITO which is identical with that used for the pixelelectrode. In a case of covering the scanning line lead with ITO, closeadhesion between ITO and a sealant causes a problem. An epoxy resin isgenerally used for the sealant. The sealant has good adhesion with aninsulative film such as made of SiN and can maintain a favorable sealingproperty. However, in a case where the sealant is in direct contact withthe conductive film such as an ITO film, reliability of sealing is notalways known.

As in the constitution described in JP-A No. 2005-275054, when thescanning line lead is covered with ITO that is formed at the same timewith the pixel electrode, this causes a problem for the reliabilitydepending on the relation between ITO and the sealant. Further, whilethe extent of covering the region of the peripheral ITO gives asignificant effect on the shielding effect to the scanning line leads,JP-A No. 2005-275054 has no descriptions for such a problem.

Further, in the constitution of JP-A No. 2005-275054, since ITO used forshielding the scanning line lead is identical with that used for thepixel electrode, it can not be formed continuously from the displayregion, to result in a portion where the scanning line lead is notcovered with ITO at the boundary between the scanning line and thescanning line lead portion. Then, the effect of scanning signals isgenerated from the portion not covered with ITO.

The present invention intends to eliminate blanking due to the effect ofscanning in the display region in a liquid crystal display device of theIPS system, while maintaining the sealing reliability by a sealant.

SUMMARY OF THE INVENTION

The present invention intends to overcome the problems described abovein accordance with the specific constitutions described above.

(1) A liquid crystal display device in which a liquid crystal layer isput between a TFT substrate having a first electrode formed in a planarshape, a second electrode disposed above the first electrode by way ofan insulative film, and a display region where pixels each formed with aTFT are arranged in a matrix, and a counter substrate opposed to the TFTsubstrate and formed with a color filter, and the liquid crystal layeris sealed by a sealant formed at the periphery of the TFT substrate andthe counter substrate,

wherein scanning lines are extended in a first direction and arranged ina second direction, and video signal lines are extended in the seconddirection and arranged in the first direction in the display region,

scanning line leads that connect the scanning lines with a scanning linedriving circuit are formed to the outside of the display region,

a shield electrode formed coplanar with the first electrode is extendedas far as a portion below the sealant while covering the scanning lineleads, and the insulative film is present between the shield electrodeand the sealant, and

a potential identical with a potential of the first electrode is appliedto the shield electrode.

(2) The liquid crystal display device according to (1) described above,wherein the second electrode is an interdigitated electrode.

(3) The liquid crystal display device according to (1) described above,wherein a portion overlapped with the sealant and a portion notoverlapped therewith in a planar view are present in the shieldelectrode, and a width L1 for the overlapped portion and a width L2 forthe non-overlapped portion are defined as: L2>L1.(4) The liquid crystal display device according to (1) described above,wherein video signal line leads that connect the video signal lines witha video signal driving circuit are formed to the outside of the displayregion, and the shield electrode does not cover the video signal lineleads.(5) The liquid crystal display device according to (1) described above,wherein the first electrode and the shield electrode are formed as acontinuous film.(6) A liquid crystal display device in which a liquid crystal layer isput between a TFT substrate having a first electrode formed in a planarshape, a second electrode disposed above the first electrode by way ofan insulative film, and a display region where pixels each formed with aTFT are arranged in a matrix, and a counter substrate opposed to the TFTsubstrate and formed with a color filter, and the liquid crystal layeris sealed by a sealant formed at the periphery of the TFT substrate andthe counter substrate,

wherein scanning lines are extended in a first direction and arranged ina second direction, and video signal lines are extended in the seconddirection and arranged in the first direction in the display region ofthe TFT,

scanning line leads that connect the scanning lines with a scanning linedriving circuit are formed to the outside of the display region,

a shield electrode formed coplanar with the first electrode is extendedas far as a portion below the sealant while covering the scanning lineleads, and the insulative film is present between the shield electrodeand the sealant, and

a potential identical with a potential of the second electrode isapplied to the shield electrode.

(7) The liquid crystal display device according to (6) described above,wherein the second electrode is an interdigitated electrode.

(8) The liquid crystal display device according to (6) described above,wherein a portion overlapped with the sealant and another portion notoverlapped therewith in a planar view are present in the shieldelectrode, and a width L1 for the overlapped portion and a width L2 forthe non-overlapped portion are defined as: L2>L1.(9) A liquid crystal display device in which a liquid crystal layer isput between a TFT substrate having a first electrode formed in a planarshape, a second electrode disposed above the first electrode by way ofan insulative film, and a display region where pixels each formed with aTFT are arranged in a matrix, and a counter substrate opposed to the TFTsubstrate and formed with a color filter, and the liquid crystal layeris sealed by a sealant formed at the periphery of the TFT substrate andthe counter substrate,

wherein scanning lines are extended in a first direction and arranged ina second direction, and video signal lines are extended in the seconddirection and arranged in the first direction in the display region ofthe TFT,

a scanning line driving circuit is disposed to the outside of thesealant in the second direction, and scanning line leads for connectingthe scanning lines with the scanning line driving circuit are extendedin the second direction to the outside of the display region,

a shield electrode formed coplanar with the first electrode is extendedas far as a portion below the sealant while covering the scanning lineleads, and the insulative film is present between the shield electrodeand the sealant, and

a potential identical with a potential of the first electrode is appliedto the shield electrode.

(10) The liquid crystal display device according to (9) described above,wherein the scanning line leads extending in the second direction areformed below the sealant, and an insulative film is present between thesealant and the scanning line leads.

(11) The liquid crystal display device according to (9) described above,wherein the scanning line leads include first scanning line leads andsecond scanning line leads formed in a layer different from the firstscanning line lead by way of an insulative film, and an insulative filmis present between the first scanning line leads and the second scanningline leads, and the sealant.(12) A liquid crystal display device in which a liquid crystal layer isput between a TFT substrate having a first electrode formed in a planarshape, a second electrode disposed above the first electrode by way ofan insulative film, and a display region where pixels each formed with aTFT are arranged in a matrix, and a counter substrate opposed to the TFTsubstrate and formed with a color filter, and the liquid crystal layeris sealed by a sealant formed at the periphery of the TFT substrate andthe counter substrate,

wherein scanning lines are extended in a first direction and arranged ina second direction, and video signal lines are extended in the seconddirection and arranged in the first direction in the display region,

a scanning line driving circuit is disposed to the outside of thesealant in the second direction, and scanning line leads for connectingthe scanning lines with the scanning line driving circuit are extendedin the second direction to the outside of the display region,

a shield electrode formed coplanar with the first electrode is extendedas far as a portion below the sealant while covering the scanning lineleads, and the insulative film is present between the shield electrodeand the sealant, and

a potential identical with a potential of the second electrode isapplied to the shield electrode.

(13) The liquid crystal display device according to (12) describedabove, wherein the scanning line leads extending in the second directionare formed below the sealant, and an insulative film is present betweenthe sealant and the scanning line leads.

(14) The liquid crystal display device according to (12) describedabove, wherein the scanning line leads include first scanning line leadsand second scanning line leads formed in a layer different from thefirst scanning leads by way of an insulative film, and an insulativefilm is present between the first scanning line leads and the secondscanning line leads, and the sealant.

According to the invention, since the scanning line leads for supplyinga gate voltage to the scanning lines are covered with the shieldelectrode applied with a common voltage, charging to the commonelectrode by the gate voltage can be prevented, and a blankingphenomenon generated at the periphery of the display region due to thecharging by the counter substrate can be prevented.

Further, in the invention, since the shield electrode is extended as faras the portion below the sealant, effect of the gate electrode appliedto the scanning line leads can be prevented more reliably. Further, inthe invention, since the insulative film is disposed between the shieldelectrode and the sealant, deterioration of the sealing effect for thesealant can be prevented.

DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS

FIG. 1 is a plan view of a liquid crystal display device according tothe present invention;

FIG. 2 is a cross sectional view of the liquid crystal display device ofthe invention;

FIG. 3 is a plan view of the pixel electrode shown in FIG. 2;

FIG. 4 is a plan view of a TFT substrate of the liquid crystal displaydevice of the invention;

FIG. 5 is a cross sectional view of a liquid crystal display device of acomparative embodiment;

FIG. 6 is a plan view of a TFT substrate of the liquid crystal displaydevice of the comparative embodiment; and

FIG. 7 is a cross sectional view of a liquid crystal display device as asecond embodiment of the invention.

PREFERRED EMBODIMENTS OF THE INVENTION

The present invention is to be described specifically by way of thefollowing preferred embodiments.

Embodiment 1

FIG. 1 is a plan view of a liquid crystal display device applied withthe present invention which is used, for example, in cellular phones. InFIG. 1, a counter substrate 200 is disposed above a TFT substrate 100. Aliquid crystal layer is put between the TFT substrate 100 and thecounter substrate 200. The TFT substrate 100 and the counter substrate200 are bonded by a sealant 20 formed to a frame portion. The TFTsubstrate 100 is made larger than the counter substrate 200, in which aterminal portion 150 for supplying a power source, video signals,scanning signals, etc. to the TFT substrate 100 is formed to a portionof the TFT substrate which is made larger than the counter substrate200.

Further, an IC driver 50 for driving scanning lines, video signal lines,etc. are disposed to the terminal portion 150. The IC driver 50 isdivided into three regions in which a video signal driving circuit 52 isdisposed at a central portion and scanning signal driving circuits 51are disposed on both sides of them.

In the display region 10 shown in FIG. 1, unillustrated scanning linesare extended in the lateral direction and arranged in the verticaldirection. Further, unillustrated video signal lines are extended in thevertical direction and arranged in the lateral direction. The scanninglines are connected by way of the scanning line leads 31 to the scanningsignal driving circuits 51 of the IC driver 50. In FIG. 1, since thedisplay region 10 is arranged at the central portion of the liquidcrystal display device, the scanning line leads 31 are disposed on bothsides of the display region 10 and, accordingly, the scanning linedriving circuits 51 are disposed on both sides of the IC driver 50. Onthe other hand, video signal line leads 41 that connect the video signallines with the IC driver 50 are gathered on the lower side of thescreen. The video signal line leads 41 are connected with the videosignal driving circuit 52 disposed at the central portion of the ICdriver 50.

Since the scanning signals supply a gate voltage for turning TFT on oroff, this voltage is high. Accordingly, the scanning signals more tendto cause noises in the inside of the liquid crystal display devicecompared with video signals, etc. Particularly, the periphery of thescreen where the scanning line leads 31 are present is liable to undergothe effect of the scanning signals as will be described later. As aresult, blanking 11 occurs in a region as shown by dotted lines inFIG. 1. The portion for the blanking 11 is in a state where the contrastis deteriorated.

FIG. 2 is a cross sectional view showing the constitution of theinvention which is adapted so as not to cause such blanking. The liquidcrystal display device shown in FIG. 2 is a liquid crystal displaydevice of an IPS system. FIG. 4 is a plan view of a TFT substrate in theidentical liquid crystal display device. The liquid crystal device inFIG. 2 includes a section divided from the right side thereof into apixel area A that constitutes a portion of a display region 10, a commonwiring connection area B that connects a common wiring 60 with a shieldelectrode 107 or a common electrode 108, and a scanning line lead areaC. As shown in FIG. 4, since the common electrode 108 and the shieldelectrode 107 are formed as a continuous film, when a common voltage issupplied to the shield electrode 107, the common voltage is alsosupplied simultaneously to the common electrode 108.

At first, the constitution of the pixel area in FIG. 2 is to bedescribed. In FIG. 2, a gate electrode 101 is formed above a TFTsubstrate 100 formed of glass. The gate electrode 101 is formed coplanarwith the scanning lines 30. The gate electrode 101 includes an Al alloyand an Mo alloy stacked thereon.

A gate insulator 102 is formed of SiN while covering the gate electrode101. A semiconductor layer 103 is formed of an a-Si film above the gateinsulator 102 at a position opposing to the gate electrode 101. The a-Sifilm is formed by plasma CVD. The a-Si film forms a channel portion ofthe TFT, and a source electrode 104 and a drain electrode 105 are formedabove the a-Si film while putting the channel portion therebetween. Anunillustrated n⁺Si layer is formed between the a-Si film and the sourceelectrode 104 or the drain electrode 105 for establishing an ohmiccontact between the semiconductor layer 103 and the source electrode 104or the drain electrode 105.

The source electrode 104 is used also as video signal lines 40, and thedrain electrode 105 is connected with a pixel electrode 110. The sourceelectrode 104 and the drain electrode 105 are formed as a coplanar layersimultaneously. In this embodiment, the source electrode 104 and thedrain electrode 105 are formed of an Mo alloy. When it is intended tolower the electric resistance of the source electrode 104 or the drainelectrode 105, an electrode structure, for example, including an Alalloy sandwiched between Mo alloys is used.

An inorganic passivation film 106 is formed of SiN and disposed whilecovering the TFT. The inorganic passivation film 106 protects TFT,particularly, the channel portion thereof against impurities. While anorganic passivation film may be formed above the inorganic passivationfilm 106, only the inorganic passivation film 106 is used in thisembodiment.

A common electrode 108 is formed above the inorganic passivation film106. The common electrode 108 is formed by sputtering ITO (indium tinoxide) as a transparent conductive film over the entire display region10. That is, the common electrode 108 is formed in a planar shape. Afterforming the common electrode 108 by sputtering over the entire surface,only the through hole portion for conducting the pixel electrode 110 andthe drain electrode 105 is removed by etching the common electrode 108.In this case, the shield electrode 107 to be described later is formedsimultaneously.

An upper insulative film 109 is formed of SiN and disposed whilecovering the common electrode 108. After forming the upper insulativefilm 109, through holes are formed by etching. A first through hole TH1is formed by etching the inorganic passivation film 106 using the upperinsulative film 109 as a resist. Then, ITO is formed as the pixelelectrode 110 by sputtering while covering the upper insulative film 109and the first through hole TH1. The pixel electrode 110 is formed bypatterning the sputtered ITO. ITO as the pixel electrode 110 isdeposited also to the first through hole TH1, the second through holeTH2, and the third through hole TH3 simultaneously and patternedsimultaneously to form a connection electrode 111 in the second throughhole TH2 and the second through hole TH3. In the first through hole TH1,the drain electrode 105 extended from the TFT and the pixel electrode110 conduct with each other, and video signals are supplied to the pixelelectrode 110.

FIG. 3 shows an example of the pixel electrode 110. The pixel electrode110 is an interdigitated electrode closed at both ends. A slit 112 isformed between digits. Below the pixel electrode 110, an unillustratedplanar common electrode 108 is formed. When the video signals areapplied to the pixel electrode 110, liquid crystal molecules 301 arerotated by lines of electric force generated between the commonelectrode 108 and the pixel electrode 110 through the slit 112. Thiscontrols a light that passes through the liquid crystal layer 300 toform images.

The pixel area in FIG. 2 explains the state in the cross sectional view.The slit 112 is defined between adjacent interdigitated electrodes. Acommon voltage is applied to the common electrode 108 and a voltage bythe video signal is applied to the pixel electrode 110. When the voltageis applied to the pixel electrode 110, as shown in FIG. 2, lines ofelectric force are generated to rotate the liquid crystal molecules 301in the direction of the lines of electric force to thereby control thetransmittance of a light from a back light. Since the lighttransmittance from the back light is controlled on every pixels, imagesare formed. An alignment film 113 is formed above the pixel electrode110 for aligning the liquid crystal molecules 301.

In FIG. 2, a counter substrate 200 is disposed while sandwiching aliquid crystal layer 300 relative to the TFT substrate. A color filter201 is formed at the inside of the counter substrate 200. As the colorfilter 201, red, green, and blue color filters 201 are formed on everypixels to form color images. A black matrix 202 is formed between acolor filter 201 and another color filter 201 adjacent thereto toimprove the contrast of images. However, since FIG. 2 is a crosssectional view for the periphery of the display region 10, the colorfilter 201 is shown only for one color and a most portion is coveredwith the black matrix 202 as a light shielding film.

An over coat film 203 is formed while covering the color filter 201 andthe black matrix 202. Since the surface of the color filter 201 and theblack matrix 202 is uneven, the surface is planarized by the overcoatfilm 203. An alignment film 113 for aligning the liquid crystalmolecules 301 is formed on the overcoat film 203. Since FIG. 2 shows theIPS, the common electrode 108 is formed on the side of the TFT substrate100 and not formed on the side of the common electrode 200.

As shown in FIG. 2, a conductive film is not formed to the inside of thecounter substrate 200 in the IPS system. Then, the potential of thecounter substrate 200 becomes instable. Further, electromagnetic noisesfrom the outside intrude into the liquid crystal layer 300 to giveundesired effects on the images. In order to eliminate such a problem, asurface conductive film 210 is formed to the outside of the countersubstrate 200. The surface conductive film 210 is formed by sputteringITO as a transparent conductive film.

As described above, while electromagnetic noises, etc. from the outsideof the liquid crystal display device can be shielded by the surfaceconductive film 210, charges in the inside of the liquid crystal displaydevice by the effect of the gate voltage or the like that are generatedin the inside of the liquid crystal display device can not be coped withby the surface conductive film 210. Such a problem is coped with by theconstitution of the invention to be described later.

A common voltage is applied to the common electrode 108 from the commonwiring 60. The common wiring 60 is formed coplanar with the scanninglines 30 or the gate electrode 101. In FIG. 2, the common electrode 108and the shield electrode 107 covering the scanning line leads 31 areformed as a continuous film as shown in FIG. 4. Accordingly, as shown inFIG. 2, when the common wiring 60 and the shield electrode 107 areconnected, the common wiring 60 and the common electrode 108 areconnected at the same time.

The common wiring 60 and the shield electrode 107 are connected asdescribed below. A through hole is formed in the upper insulative film109, the inorganic passivation film 106, and the gate insulator 102 toexpose a portion of the common wiring 60. On the other hand, a throughhole is formed in the upper insulative film 109 to expose a portion ofthe shield electrode 107. Then, when an ITO film for forming the pixelelectrode 110 is sputtered, ITO is deposited at the same time and theITO film is patterned simultaneously with the pixel electrode 110 tothereby form a connection electrode 111 and connect the shield electrode107 with the common electrode 108.

In FIG. 2, the scanning line lead area C is a portion showing thecharacteristic feature of the invention. The scanning line leads 31 inFIG. 2 have a two-layered structure. Particularly, in a small sizedliquid crystal display device, it is strongly demanded to narrow theframe portion at the periphery of the display region 10. The scanningline leads 31 are disposed in the frame portion at the outside of thedisplay region 10. In a case where the scanning line leads 31 aredisposed in a coplanar layer, it is necessary to take a distance betweeneach of the scanning line leads 31 and this imposes a limit on thenarrowing of the frame portion.

In the scanning line lead area C in FIG. 2, the space occupied by thescanning line leads 31 is decreased by disposing the scanning line leads31 separately into two layers, that is, first scanning line leads 311and second scanning line leads 312. In FIG. 2, the first scanning lineleads 311 are formed coplanar with the scanning lines 30 or the gateelectrode 101, and the second scanning line leads 312 are formedcoplanar with the video signal lines 40 or the drain electrode 105. Thescanning lines 30 and the second scanning line leads 312 are connectedby a through hole not illustrated in FIG. 2.

Since the gate insulator 102 is present between the first scanning lineleads 311 and the second scanning line leads 312, the first scanningline leads 311 and the second scanning line leads 312 can be arrangedwith no gaps therebetween or in superposition to each other in a planarview. Accordingly, the frame region can be narrowed.

A gate voltage at a relatively high voltage for turning the TFT on andoff is applied to the scanning lines 30 and the scanning line leads 31.Particularly, when the scanning line leads 31 are not covered with theshield electrode 107 or the like, a portion of the common electrode 108is charged by the effect of the gate voltage. Particularly, when theblack matrix 202 formed to the counter substrate 200 is formed of aresin or the like as an insulator, the black matrix 202 is liable to becharged. When the counter substrate 200 is charged, the effect prevailsas far as the liquid crystal layer 300 and noises are formed in thevideo signals to generate the blanking at the periphery of the screen.

In the invention, the effect of the gate voltage on the countersubstrate 200 is prevented by extending the shield electrode 107 formedsimultaneously with the common electrode 108 as far as a portion belowthe sealant 20 and completely covering the scanning line leads 31. Theshield electrode 107 is formed of an ITO film which is identical withthat used for the common electrode 108. Further, an inorganicpassivation film 106 formed of SiN is present between the secondscanning line leads 312 and the shield electrode 107.

The shield electrode 107 is covered with the upper insulative film 109.Accordingly, the sealant 20 and ITO constituting the shield electrode107 are not in direct contact with each other. Accordingly, the sealant20 is in contact with the upper insulative film 109 as an insulator toenhance the reliability for the seal portion.

The shield electrode 107 is extended to the portion below the sealant 20thereby improving the shielding effect for the scanning line leads 31.However, the shield line is not extended beyond the sealant 20 as far asthe outside. This is for preventing that the bonding strength at theboundary between the ITO film constituting the shield electrode 107 andthe upper insulative film 109 or the inorganic passivation film 106gives undesired effects on the sealing reliability.

Accordingly, for the shield electrode 107, a region L1 overlapped withthe sealant 20 and a region L2 not overlapped with the sealant 20 arepresent below the sealant 20 as shown in FIG. 2. For maintaining a highreliability of the sealing portion, it is desirable to define theregions as: L2>L1.

FIG. 4 is a plan view of the TFT substrate 100 of the liquid crystaldisplay device according to the invention. In FIG. 4, the TFT substrate100 is disposed as far as the sealant 20. The sealant 20 is shown by adotted chain. In FIG. 4, the scanning lines 30 are extended in thelateral direction and arranged in the vertical direction in the displayregion 10. Further, the video signal lines 40 are extended in thevertical direction and arranged in the lateral direction. The scanninglines 30 are connected with the scanning line leads 31 present on bothsides of the display region 10. Further, the video signal lines 40 areconnected with the video signal lines leads 41 that are present belowthe display region 10.

The scanning line leads 31 present on both sides of the display region10 are extended to a portion lower than the display region 10 andconnected with the scanning line driving circuits 51 of the IC driver50. The video signal is line leads 41 present at a lower side of thedisplay region 10 are connected with the video signal driving circuit 52which is present to a further lower side of the display region 10. InFIG. 4, the scanning lines 31 are present with no gaps to each other ina planar view. As has been described above with reference FIG. 2 such anarrangement is possible, since the scanning lines 31 have a two-layeredstructure and they are insulated from each other by the insulation film.

In FIG. 4, the common wiring 60 is extended on the right of the displayregion 10, and the common wiring 60 is connected by way of the secondthrough hole TH2 and the third through hole TH3 to the shield electrode107 and the common electrode 108 formed as a film in contiguous with theshield electrode 107. The display region 10 is entirely covered with thecommon electrode 108 and the scanning line leads 31 present on bothsides of the display region 10 are covered with the shield electrode107. The common electrode 108 and the shield electrode 107 are formed ofa continuous film and this is shown by hatched lines. Accordingly, atthe inside of the sealant 20, the scanning lines 30 and the scanningline leads 31 are entirely covered with the common electrode 108 or theshield electrode 107 formed of ITO. While the shield electrode 107covers the scanning line leads 31, it does not cover the video signalline leads 41. This is because the video signal voltage is low and thesignal is unlikely to charge the counter substrate 200. When the shieldelectrode 107 covers the video signal line leads 41, the capacitancebetween the video signal line leads 41 is increased to possibly giveundesired effects on the processing speed of the video signals dependingon the case.

The shield electrode 107 is overlapped with the sealant 20 in a planarview. The amount of overlap between the sealant 20 and the shieldelectrode 107 is L1, while the amount of non-overlap between them is L2.As has been described with reference to FIG. 2, the amounts are definedas: L2>L1 in this embodiment. Further, the upper insulative film 109formed of SiN is present between the shield electrode 107 and thesealant 20 to ensure the reliability of sealing.

The scanning line leads 31 are present also below the sealant 20, inorder to decrease the width of the frame. However, in a case of thefirst scanning line leads 311 formed coplanar with the gate electrode101, three layers of insulative films, that is, the gate insulator 102,the inorganic passivation film 106, and the upper insulative film 109are present between the sealant 20 and the leads 31. In the case of thesecond scanning line leads 312 formed coplanar with the drain electrode105, two layers of insulative films, that is, the inorganic passivationfilm 106 and the upper insulative film 109 are present between thesealant 20 and the leads 31. Accordingly, the sealant is in contact withthe insulators and sealing failure does not occur.

As has been described above, according to this embodiment, since thescanning line leads 31 are entirely covered with the shield electrode107 at the inside of the sealant, this can avoid the problem that thecommon electrode 108 is charged by the gate voltage. Further, since theshield electrode 107 is formed in contiguous with the common electrode108 formed in the planar shape, the shield electrode 107 and the commonelectrode 108 formed in the display region 10 can be connected with nodiscontinuity and, accordingly, the shield effect is excellent.

Further, according to this embodiment, since the shield electrode 107formed of ITO and the sealant 20 are not in direct contact but thesealant 20 is in contact only with the insulative film, reliability forthe sealing portion is not deteriorated.

FIG. 5 shows a comparative embodiment to the invention. Like FIG. 2,FIG. 5 is a cross sectional view for the periphery of the liquid crystaldisplay device shown in FIG. 1. The constitution of FIG. 5 is identicalwith the constitution of FIG. 2 except for the shield electrode 107. InFIG. 5, the shield electrode 107 is not overlapped with the sealant 20,but a region d where the scanning line leads 31 are opposed to thecounter substrate 200 by way of the inorganic passivation film 106 andthe upper insulative film 109 is present between the inside of thesealant 20 and the end of the shield electrode 107. Accordingly, theinside of the counter substrate 200 is charged under the effect of thegate potential in the region d. Then, the effect of the charge at theinside of the counter substrate 200 exerts on the liquid crystal layer300 to generate the blanking at the periphery of the screen as shown inFIG. 1.

FIG. 6 is a plan view for a TFT substrate 100 in the comparativeembodiment. The constitution in FIG. 6 is identical with that in FIG. 4except for the range of a shield electrode 107. In FIG. 6, a sealant 20is formed at the periphery of a TFT substrate 100. The sealant is shownby a dotted chain. Scanning line leads 31 are disposed on both sides ofa display region 10. The shield electrode 107 does not cover the insideof the sealant 20 and the end of the display region 10 entirely but itcovers only a portion thereof. That is, a region d where the scanningline leads 31 are not covered is present at the inside of the sealant20. Then, the inside of the counter substrate 200 is charged by the gatevoltage applied to the scanning line leads 31 in the region d and, ashas been described with reference to FIG. 5, blanking occurs at theperiphery of the display region 10. As described above, even when theshield electrode 107 is disposed above the scanning line leads 31coplanar with the common electrode 108, no sufficient effect can beobtained against the blanking unless the shield electrode 107 isextended as far as the overlap range between the shield electrode 107and the sealant 20.

Embodiment 2

In the liquid crystal display device of the IPS system of Embodiment 1,the planar common electrode 108 is formed above the inorganicpassivation film 106, the upper insulative film 109 is formedthereabove, and the interdigitated pixel electrode 110 is formed furtherthereabove. Contrary to the arrangement of the electrodes in the liquidcrystal display device of Embodiment 1, a planar pixel electrode 110 maybe formed on the inorganic passivation film 106 and an interdigitatedcommon electrode 108 may be formed thereabove while sandwiching theupper insulative film 109 between them. The shape of the commonelectrode 108 in this case may be identical with that for theinterdigitated electrode shown in FIG. 3.

In FIG. 7, a planar pixel electrode 110 is formed above the inorganicpassivation film 106 in the pixel area. An upper insulative film 109 isformed above the planar pixel electrode 110, and an interdigitatedcommon electrode 108 is formed above the upper insulative film 109. Theshield electrode 107 covering the scanning line leads 31 is formed of anITO film simultaneously with the formation of the pixel electrode 110.The shield electrode 107 is formed by an ITO film simultaneously withthe pixel electrode 110. The shield electrode 107 is formedsimultaneously with the formation of the pixel electrode 110 and acommon potential is supplied from the common wiring 60 through thesecond by way of hole TH2 and the third through hole TH3 to the shieldelectrode 107. Accordingly, in the Embodiment 2, the ITO filmconstituting the pixel electrode 110 and the ITO film constituting theshield electrode 107 are not formed as a continuous film.

The constitution as shown in FIG. 7 can be formed by the followingprocess. The process is identical with that of the Embodiment 1 shown inFIG. 2 as far as the formation of the inorganic passivation film 106.After forming the inorganic passivation film 106, a first through holeTH1 is formed for connecting the pixel electrode 110 with the drainelectrode 105 of the TFT. Then, ITO is sputtered. By patterning thedeposited ITO film, the pixel electrode 110, the contact of the throughhole portion, and the shield electrode 107 are formed. In this case, thepixel electrode 110 and the shield electrode 107 are not formed as acontinuous film.

Then, the upper insulative film 109 is formed of SiN. Then, in the samemanner as in the Embodiment 1, a second through hole TH2 and a thirdthrough hole TH3 are formed. Then, ITO as the common electrode 108 isdeposited by sputtering. By patterning ITO, the interdigitated commonelectrode 108 and the contact of the through holes are formed. Among thethrough holes, only the first through hole TH1 for connecting the drainelectrode 105 with the pixel electrode 110 is different from theEmbodiment 1 in FIG. 2.

The Embodiment 2 is identical with the Embodiment 1 in that the shieldelectrode 107 is formed as far as the portion below the sealant 20 in aplanar view. Further, it is also identical with the Embodiment 1 in thatthe common voltage is applied to the shield electrode 107. Accordingly,the same effect as in the Embodiment 1 can be obtained also in theliquid crystal display device of the IPS system of a type in which theplanar pixel electrode 110 is disposed to the lower side and the commonelectrode 108 is formed thereabove in the interdigitated shape by way ofthe insulative film.

For the Al alloy forming the gate electrode, the common wiring coplanartherewith, and the second scanning line leads described previously, theAl alloy may be replaced with an AlNd alloy or the Mo alloy may bereplaced with an MoCr alloy. In the same manner, for the sourceelectrode or the drain electrode, the Mo alloy may be sandwiched withMoCr alloys, or the AlNd alloy may be sandwiched with MoCr alloys. It isevident that the alloys described above are not limitative but astructure in which other pure metals or alloys are laminated may also beadopted.

Further, in FIG. 4, FIG. 6, etc., a common voltage is supplied from thecommon wiring to the shield electrode 107 or the common electrode 108 inthe common wiring connection portion at the outside of the displayregion. However, it is not particularly restricted thereto, but thecommon wiring 60 may be disposed in parallel with the scanning lines 30in the display region and a common wiring connection portion ofsupplying a common voltage to the shield electrode 107 or the commonelectrode 108 may be disposed in the display region. This can stabilizethe potential of the common electrode 108 in the display region.Further, it may also be adopted such that the common wiring connectionportion outside of the display region shown in the drawing is notdisposed, but the common voltage may be supplied from the common wiring60 to the shield electrode 107 and the common electrode 108 only by thecommon wiring connection portion in the display region describedpreviously. This can decrease the area at the outside of the displayregion.

Further, while the second through hole TH2 and the third through holeTH3 are disposed in combination in the first direction in the commonwiring connection portion, they may also be disposed in combination inthe second direction. This can decrease the area at the outside of thedisplay region.

As shown in FIG. 4 in this embodiment, crossing between the scanninglines 30 and the common wiring 60 is prevented by driving the scanninglines 30 on the side closer to the terminal portion of the displayregion by way of the scanning line leads 31 disposed on the right of theTFT substrate, and driving the scanning lines 30 on the side remote fromthe terminal portion of the display region by way of the scanning lineleads 31 disposed on the left of the TFT substrate and providing acommon wiring between the display region and the scanning line leads 31on the left of the TFT substrate. However, the common wirings 60 may bedisposed on both right and left sides of the display region and thecommon wiring connection portion may be disposed to each of them.

In this embodiment, as shown in FIG. 4, FIG. 6, etc., the common wiring60 is disposed between the scanning line leads 31 and the video lineleads 41 at the terminal portion. While the shield electrode 107 coversthe scanning line leads 41, it does not cover the common wiring 60.

The invention claimed is:
 1. A display device comprising: a firstsubstrate; a second substrate opposite the first substrate, the secondsubstrate including a first electrode having a planar shape, a secondelectrode over the first electrode, an insulative film between the firstelectrode and the second electrode, and a display region in which pixelsformed with a TFT are arranged in a matrix; first lines extending in afirst direction and arranged in a second direction; second linesextending in the second direction and arranged in the first direction inthe display region; first line leads configured to connect the firstlines with a first line driving circuit outside the display region; anda third electrode coplanar with the first electrode, the third electrodehaving a portion extending below a sealant at a periphery of the firstsubstrate and the second substrate and over the first line leads,wherein the insulative film is between the third electrode and thesealant, and the third electrode is arranged such that if a potential isapplied to the first electrode, an identical potential is applied to thethird electrode.